水汽处理对量子点发光二极管的性能影响研究

Effect of Water Vapor Treatment on the Performance of Quantum Dot Light-Emitting Diodes

在量子点电致发光二极管(quantum-dot light-emitting diodes, QLEDs)的研究中,外界空气尤其是水氧一直是影响器件性能的主要因素。而有研究表明水是导致QLED器件固定电流下亮度提升的原因之一,因此通过水汽处理的方式对这一效果进行提升有利于进一步优化器件性能。主要基于水对量子点表面缺陷态的钝化作用来研究水汽处理量子点发光层对电致发光器件整体性能的影响,并探索最佳处理时间。首先利用全溶液法制备了一系列QLED器件,并在制备过程中对量子点膜层进行水汽处理,通过保持湿度不变改变处理时长的方式改变水汽处理程度。然后对各个器件进行电致发光光谱的表征,结果表明经过水汽处理的QLED器件的电致发光光谱相对未处理器件有一定程度的蓝移,并且随着处理时间的延长蓝移程度增大,分析发现这是水分子氧化量子点引起表面钝化从而减少带边缺陷态发光的结果。此外,通过测量各个器件的电流密度-电压-亮度(J-V-L)曲线对比不同水汽处理时长下器件的电流密度和发光强度大小,并通过计算得到各器件的电流效率曲线。结果表明随着处理时间的延长, QLED器件的亮度和电流效率都取得较大幅度的提升,处理时长为3 min时亮度提升10%,电流效率提升50%。最后,利用寿命测试设备对器件进行老化,得到不同处理时长器件在相同固定电流密度下亮度随时间变化的曲线。结果表明各个器件亮度均表现出先提升后下降的过程,亮度初始提升幅度约为50%~70%,并且提升到最大值所用时长随处理时间的增大而减小,说明水汽处理对器件亮度提升更有效。通过寿命公式计算器件的寿命并进行对比,发现经水汽处理器件寿命相对未处理器件最高提升了70%。总之,水汽处理对QLED器件的性能在一定程度上起优化作用,这对于QLED器件效率和寿命的提升以及封装工艺的简化是十分有益的。

In the study of Quantum-Dot Light-Emitting Diodes(QLEDs), theambient air, especially water and oxygen, has been a major factor affecting device performance. However, some phenomena have shown that water is one of the causes of the increase of luminance under the certain current of QLEDs. Therefore, this effect can be improved by water vapor treatment to optimize device performance greatly. This work aims to study the effect of water vapor treatment to the performance of Quantum-Dot Light-Emitting Diodes(QLED) based on the passivation of the surface states of the quantum dots by water and explore the best processing time. Firstly, The QLEDs were fabricated through solution processes, and after the fabrication of the emission layer, the QLEDs were placed in the argon atmosphere with a certain humility. In this progress, the degree of water vapor treatment was depended by the different processing time, and the effect of air was isolated by the argon atmosphere. Secondly, the electroluminescence spectra of each device were characterized. The results show that the spectrum of treated QLEDs has a slight blue shift and the shift increases with the increase processing time. The reason for the blue shift is that the particle sizes of QDs decrease due to the oxidation of the surface states of the quantum dots by water. In addition, the current density-voltage-luminance(J-V-L) curves were characterized. The luminance and current intensity of each device was compared, and the current efficiency-current intensity(CE-J) curves were obtained. The results show that the luminance and CE of QLEDs with water vapor treatment were greatly improved with the extension of the processing time.(The luminance is increased by 10%, and the CE is increased by 50% when the processing time is 3 mins) In the end, the luminance of all QLEDs in the certain current were tested and the luminance-time curves were obtained. The aging curves show that the luminance of each QLEDsincreasedbefore the deterioration of each device. The initial luminance of devices was improved by 50% to 70% and the time taken to increase to the maximum value decreased with the extension of processing time. The results indicate that the water vapor treatment is effective to optimize the performance of QLEDs. The lifetime of all devices wascalculated by the life formula, and the comparison of each deviceshows that the treated devices have a longer life than others.(The lifetime is about 1.7 times of the untreated device) As the processing time increases,the decrease of the maximum luminance and the intensifieddeteriorationare attributed to the negative effects on the organic materials of water and the new defect states generated during the oxidation of the quantum dots by the water molecules.In summary, the water vapor treatment optimizes the performance of QLEDs, which is beneficial for the research of the aging mechanism of the QLEDs and the simplification of the packaging process.